Slab Deformation Research Articles

Influence of concrete topping on behaviour of prestressed Hollow Core floor slabs on flexible supports

Slim Floors (SF) are the structures made of the Hollow Core (HC) slabs supported on the slender beams, where the beam height is usually slightly greater than the height of precast slab element. With the increase of the supports' deflection, the deformation of the HC slab occurs, and in consequence, additional transverse normal and shear stresses appear in the precast element, which can cause a diagonal cracking and destruction of external webs of this element. It may also result in longitudinal cracks on bottom surface of the slab. Despite the frequent implementation of this type of structures, the existing standard EN 1168 gave only a brief record of the need to take the reduction in design shear capacity into account, but is not given any calculation procedure.
 It is widely believed that reduction of unfavourable effects of shear stress in the HC slab’s web can be achieved by filling the cores with concrete or arrangement of the monolithic layer or concrete topping. The fib guidelines are practically the only one document which allows to determine the shear capacity of SF slabs, including the influence of concrete topping or core filling – brief description of this design model is presented in the paper. In order to determine the effect of concrete topping on the behaviour of prestressed HC slabs on the flexible supports, a number of calculation analyzes were performed, which take into account the effects of thickness of the concrete topping, the value of the friction coefficient between the concrete topping and the precast element, the sequence of concreting of vertical joints and topping layer and the amount of supplementary reinforcement in the topping. The results of the calculations, and the conclusions derived from them, are presented in the article.

Evaluation of Temperature-Induced Curling in Concrete Slabs Using Deflection Difference Analysis

The curling and warping of rigid pavements are the results of temperature and moisture gradients varying with depth, creep, and other factors, including construction. The indicators commonly used to evaluate slab deformation include a combination of deflections derived from a heavy-weight deflectometer (HWD) that are measured at specific locations on pavement slabs. Indicators comprise the sum of deflections (SD) across the joints and the impulse stiffness modulus (ISM) deflection ratio. The objective of this study was to identify the best indicator that can be employed for assessing the slab curling level relationship to temperature. The study was included in a project developed by the U.S. Army Engineer Research and Development Center (ERDC) and sponsored by the Federal Aviation Administration (FAA). At selected military bases, HWD testing on concrete slabs was executed on two different occasions toward the end of summer and in winter. These tests were conducted to monitor slab deflections under different temperature conditions to quantify a correlation between measured deflections and temperature. The analysis showed that the SD rather than the ISM ratio could be adopted as an indicator to determine the relative degree of slab curling. The proposed approach to analyze deflection parameters showed promising results, and with a dedicated database and intensive testing, it is believed possible to refine the regression analysis and increase its level of determination. The proposed methodology for analyzing SD and temperature differences can be adopted in those cases intended to evaluate curling trend relationships to construction or curing techniques.

Investigation on slab continuous straightening technology and deformation analysis

A new method of setting continuous bending and straightening strain rate according to temperature subzone was brought forward. By making use of the high temperature creep character effectively during the continuous casting slab being straightened, a new model curve of continuous caster was developed. And by using theoretical and finite element method the strain and strain rate of the slab under multi-point straightening and the new continuous straightening were analysed. The result shows that for continuous straightening the strain rate of the slab is constant and lower than that of the slab under multi-point straightening, and the strain varies linearly. It is verified that the new continuous straightening technology is reasonable and superior.

The technical state of earth dams in Lithuania

AbstractDams are ageing out as all constructions do, and inaccuracies during the field survey, designing and construction, as well as defects of building materials and deterioration due to environmental impacts accelerate the aging process. The article presents the technical state assessment comparable results of 260 Lithuanian earth dams performed in 2002–2009 and 368 dams in 1997; the analysis of character and causes of the main deteriorations and defects. The typical causes of failure (according to their danger to the stability of the entire hydroscheme) are: diverse intensity of seepage water leakage at the downstream slope and the tailwater of dam; landslides and deformation of the slopes of the dams; bigger cracks, deformation, tilt in shaft spillway; scour, deformation of dam slope protection slabs, concrete cover layer deterioration, collapsing of junctures are mainly caused by the environmental (frost cycles; ice, wave blows; moss, grass, bushes roots; periodical wetting, etc.) impacts.

3차원 수치해석을 통한 개착터널내 단면변화구간의 손상미케니즘 연구

본 연구는 터널의 단면변화구간에서 발생한 손상 미케니즘에 대하여 이루어졌다. 이를 위해 단면변화 구간을 대상으로 다양한 현장조사 및 시험을 실시하였으며, 이를 바탕으로 2차원 및 3차원 수치해석을 수행하였다. 현장조사 및 시험 결과, 슬래브 손상에 대한 직접적인 원인을 찾을 수 없었으며, 2차원 수치해석을 수행한 결과 기준 안전율(1.0)을 만족하는 것으로 분석되었다. 추가로 수행한 3차원 수치해석 결과, 기둥 간격의 변화에 따라 슬래브 휨응력 변화를 전달시키지 못해 손상이 발생한 것으로 분석되었다. 보강을 위해 터널내 기둥을 추가하는 방안을 적용하였으며 그 결과, 상부 슬래브 비틀림 형상이 완화되어 보강 효과를 확인할 수 있었다. 단면 변화 구간의 경우 2차원 뿐만 아니라, 3차원으로 영향범위를 고려하여 설계에 반영한다면, 합리적이고 안정적으로 건설 및 유지관리가 가능할 것으로 판단된다. 추후에는 개착터널내 단면변화 구간에서 구조물에 영향을 최소화할 수 있는 보강방안에 대해 연구를 계속하고자 한다. This study made progress about Demage Mechanism of Transition Section in Cut and Cover Tunnel. For this study, Inspection and test was carried out about Transition Section. After this process, Numerical Analysis was accomplished by 2D, 3D. A result of inspection and test, It couldn't find the reason why the upper slab Demage was detected. So 2D Numerical Analysis was conducted. It was analyzed that the Safety Factor(1.0) was satisfied in 2D. But, the result of 3D Numerical Analysis, The reason was found that the Demage on upper slab was caused by moment change. The Moment was changed by column interval transition. For Retrofitting, Column was added under slab in tunnel. It was found that the addition column decreased upper slab deformation. After this study, It could be find that are important 3D Numerical Analysis as well as 2D Numerical Analysis in case of Transition Section. This Study can help developing construction and maintenance about Tunnel. Finally, It's going to study Retrofitting plans which have minimum influence of Transition Section in Cut and Cover Tunnel.

Crustal deformation of the Andean foreland at 31° 30′S (Argentina) constrained by magnetotelluric survey

Twenty-five new long-period magnetotelluric sites near 31.5°S were collected in a west–east profile. This profile and the previous one, aligned with and adjacent to the eastern end, have been merged to form a single profile of more than 700km long, extending from the Precordillera to the Chaco-Pampean Plain.The geotectonic scenario is characterized by a modern flat subduction zone of the Nazca plate located at a depth of around 120km and clearly defined by the distribution of earthquake hypocenters recorded by local and regional networks. A “bulge” shape at 68.5°W, with an anomalous dip to the west, is observed within this segment. The smooth slab deformation might result from the restriction on eastward motion due to the presence of an electrically resistive zone. The magnetotelluric model shows that this thick zone of increased resistivity is found from shallow crustal levels to upper mantle depths. The bulge geometry allows hot fluids and volatiles to rise from the deeper asthenospheric wedge, and reach the lower crust reducing its viscosity and letting it flow. The zones of low resistivity in the lower crust show spatial correlation with the areas of foreland deformation from Precordillera to the Sierras Pampeanas and may also suggest a ductile regime.Shear zones reactivated by Cenozoic faulting must necessarily have their roots in the levels of the ductile lower crust associated to conductive channels. The zone where the lower crust is closer to the surface coincides with the areas of greatest structural relief and erosion. The interface between the folded ductile lower crust and the brittle upper crust might act as the main level of décollement of the bordering structures between the Precordillera, Sierra de Pie de Palo and the Sierras Pampeanas. In addition, the geometry of the interface might be conditioning the vergence of those structures.

Complex mantle flow around heterogeneous subducting oceanic plates

The foundering of oceanic lithospheres controls the circulation patterns of the mantle around subducting slabs. Here, we investigate the sensitivity of the mantle flow to slab buoyancy variations along convergent margins using three-dimensional numerical models of subduction in a viscous mantle. The models illustrate that in a buoyancy-driven system varying subduction velocity arising from negative buoyancy variations effectively drives pressure gradients and confers a general flow component sub-parallel to the margin's strike, allowing for material transport over large distances around the slabs. The along-slab velocity component introduces widespread horizontal simple shear in the mantle flow which is maximized beneath the slab between ∼100 and ∼350km. Mantle flow complexities develop rapidly, although not instantaneously, upon subduction of heterogeneous plates. The resulting slab pull gradients are mostly accommodated by internal slab deformation, decoupling the mantle flow from motions at surface. Moderate slab pull variations have a minor impact on plate velocity, and might not result in trench motions, although effectively rearrange the flow. Slab buoyancy heterogeneities are firstly associated with age-dependent thickness variations, but also with slab break offs and windows, varying depth of subduction and entrainment of buoyant blocks. Because these are observed at all subduction zones, the process shown here should have a global relevance for the flow around slabs.

Controls of faulting and reaction kinetics on serpentinization and double Benioff zones

The subduction of partially serpentinized oceanic mantle may potentially be the key geologic process leading to the regassing of Earth's mantle and also has important consequences for subduction zone processes such as element cycling, slab deformation, and intermediate‐depth seismicity. However, little is known about the quantity of water that is retained in the slab during mantle serpentinization and the pattern of serpentinization that may occur during bending‐related faulting; an initial state that is essential for quantifying subsequent dehydration processes. We present a 2‐D reactive‐flow model simulating hydration processes in the presence of faulting at the trench outer‐rise. We find that the temperature dependence of the serpentinization rate in conjunction with outer‐rise faulting results in plate age and speed dependent patterns of hydration. Serpentinization also results in a reduction in surface heat flux toward the trench caused by advective downflow of seawater into the reaction region. Observed heat flow reductions are larger than the reduction due to the minimum‐water downflow needed for partial serpentinization, predicting that active hydrothermal vents and chemosynthetic communities should also be associated with bend‐fault serpentinization. Our model results agree with previous studies that the lower plane of double Benioff zones can be generated due to dehydration of serpentinized mantle at depth. More importantly, the depth‐dependent pattern of serpentinization including reaction kinetics predicts a separation between the two Benioff planes consistent with seismic observations.

Mechanical Analysis of Link Slab in Continous Paving Layer of Simple Supported Girder Bridge

The link slab of simple supported girder bridge deck was discussed in this paper. Based on “Gernal Code of design of Highway Bridges and Culverts(JTGD60-2004)” of China and linear elastic theory the continouse paving layer was analysized under the live load, temperature variation. The deformation and tensile stress formulations of link slab were given. The conclusion can provide theoretical basis for the design of building new bridge and strengthening and repairing old bridge.

Settlement Analysis of Dock Slab on Soft Soil Foundation

According to the dock engineering, the paper analyzed the settlement and deformation of dock slab of soft soil foundation by using finite element software ADINA, and summarizes the law of the settlement and deformation based on different foundation model, to provide reference for the calculation and design of similar dock engineering.

Improved Serviceability Criteria for Steel Girder Bridges

Current AASHTO LRFD Bridge Design Specifications Service I deflection limits are in place with the purpose to prevent deformation-induced structural damage and psychological user discomfort from excess bridge vibration. Previous research has shown that deflection criterion alone is insufficient in controlling excess bridge vibrations and structural deterioration of the concrete deck. Previous research shows that natural frequency criteria better controls excess vibration than deflection criteria alone. In addition, previous research shows no significant correlation between deflection and structural deformation of the concrete deck slab. To better control excess bridge vibrations and deformation-induced structural deterioration, two new separate criteria formulations are proposed. The first formulation consists of a natural frequency criteria transformed into deflection-type terms familiar to the typical bridge engineer. The second proposed formulation directly controls the acting flexural strain in the concrete deck to control deformation-induced structural damage. The proposed serviceability criteria are applied to a database of 185 steel girder bridges. Both the as-built behavior and the design optimized behavior are examined and compared with current AASHTO serviceability criteria. The proposed user comfort and deformation-induced damage serviceability formulations are intended to be incorporated into ongoing Federal Highway Administration and bridge industry long-term bridge performance research where serviceability criteria is an important component.

Co‐seismic deformation of deep slabs based on summed CMT data

We assess the co‐seismic deformation inferred from earthquake moment tensor solutions for subducting slabs at depths greater than 50 km globally. We rotate each moment tensor into a local slab reference frame, then sum tensors within 50 km depth bins to approximate long term deformation characteristics. This builds upon previous analyses by using the up‐to‐date global Centroid Moment Tensor catalog, incorporating a more complete slab geometry, and focusing on the 3‐D aspects of slab deformation. Results show a general consistency with Isacks and Molnar (1969), who found that most slabs can be divided into intermediate‐extensional, intermediate‐extensional‐deep‐compressional, and intermediate to deep‐compressional categories. Exceptions to these three categories can be related to slab bending in the top 100 km, plate convergence that is oblique to the trench normal direction, and regions of higher focal mechanism heterogeneity. The regions of higher focal mechanism heterogeneity appear where there are along‐strike changes in slab geometry and/or evidence of double‐seismic zones. We find that the sense of deformation in the intermediate strain axis direction is opposite to that of the down‐dip direction, in agreement with Kuge and Kawakatsu (1993). By quantitative comparison to numerical models of global mantle flow, we show that these observations are consistent with deformation of viscous slabs responding to their own negative buoyancy and an upper to lower mantle viscosity increase.

Diagnosis and rehabilitation of real reinforced concrete structures in coastal areas

A diagnosis and rehabilitation study of two reinforced concrete structures located in coastal areas in two different climates is presented. Building 1 was constructed in the north of Chile in 1949, at a distance of 600 m from the coastline, in a seismic zone. Cracks, steel corrosion, loosening of concrete cover and slab deformations have been identified. Building 2 was constructed in Habana City, Cuba, in 1973. It is located at <100 m from the shore. The structure of building 1 shows severe localised damage: loosening of reinforced cover and intense reinforcement bar corrosion due to high deposits of sea salts. High chloride and sulphate content in the concrete mass, low compressive strength in walls and slabs, high level of steel corrosion and zones with the existence of rust instead of steel were reported. A structural rehabilitation project to ensure an increase in service life is not possible. On the contrary, in case of building 2, a possible rehabilitation procedure is recommended. Elimination of chloride contaminated concrete and the use of special mortar is an option, and electrochemical chloride extraction and incorporation of sacrificial anodes is another. An important conclusion is made: the use of chloride and sulphate contaminated aggregates is more dangerous than the penetration of these two contaminants from the external environment for buildings constructed in coastal zones.

FEM Simulation of the Slab Edge Rolling in Unsteady Rolling Stage

According to characteristics of adjusting width by vertical roll at a certain steel corporation, unsteady deformation of head and tail of slab during edge rolling was analyzed by FEM simulation on base of a commercial software. The effect of several process conditions on the cross-section deformation and width loss of slab were also analyzed.

Shear wave reflectivity imaging of the Nazca‐South America subduction zone: Stagnant slab in the mantle transition zone?

In this study we utilize over 5000 SS waveforms to investigate the high‐resolution mantle reflectivity structure down to 1200 km beneath the South American convergent margin. Our results indicate that the dynamics of the Nazca subduction are more complex than previously suggested. The 410‐ and 660‐km seismic discontinuities beneath the Pacific Ocean and Amazonian Shield exhibit limited lateral depth variations, but their depths vary substantially in the vicinity of the subducting Nazca plate. The reflection amplitude of the 410‐km discontinuity is greatly diminished in a ∼1300‐km wide region in the back‐arc of the subducting plate, which is likely associated with a compositional heterogeneity on top of the upper mantle transition zone. The underlying 660‐km discontinuity is strongly depressed, showing localized depth and amplitude variations both within and to the east of the Wadati‐Benioff zone. The width of this anomalous zone (∼1000 km) far exceeds that of the high‐velocity slab structure and suggesting significant slab deformation within the transition zone. The shape of the 660‐km discontinuity and the presence of lower mantle reflectivity imply both stagnation and penetration are possible as the descending Nazca slab impinges upon the base of the upper mantle.

Texture Evolution during the Cold Rolled Low Carbon Steel Sheet under CSP Technology

In this item, the low carbon steel hot sheets by compact strip production (CSP) technology were cold rolled and annealed in laboratory. texture evolution during the production process of CSP-cold rolled strip were investigated by means of the XRD. The results were as follows: After hot deformation of thin slab formed a strong γ- fibre orientation texture, the density of texture increase with the cold rolled reduction increased, especially for the negative texture {100}, in γ-fibre orientation cold rolling texture density has no significant change. Compared to the traditional process, hot rolled steel sheet has higher texture, cold-rolled steel sheet has the same texture, and after-annealing sheet has further higher texture in the CSP-cold rolling process. This study enables better understanding and control on the evolution of textures the cold-rolled steel sheet processed by CSP technique and provides theory support for exploiting the CSP the cold-rolling deep drawing steel sheet

Análise numérica e experimental de vigotas pré-moldadas em concreto armado para emprego em lajes nervuradas

One of the most common applications of precast concrete is done on ribbed slabs. A relatively recent conception emerged from precast concrete ribs with three-dimensional truss reinforcement. The use of expanded polystyrene (EPS) blocks as a core material is possible in substitution of ceramic elements. To take into account the effect of concrete cracking on slab deformation, some theoretical models were considered in this work. These models were based on the moment-curvature equation of Ghalli and Frave and of Branson, using linear and non-linear solutions, through computer programs SAP2000&reg; and ANSYS&reg;. The theoretical values were compared to experimental data of beams tested under four-point loading. Also tested was a numerical solution for three-dimensional analysis of beams, based on the element solid65 available in the program ANSYS&reg;, which allows non-linear analysis of solids with structural reinforcement as the reinforced concrete.

Effects of Temperature and Moisture Gradients on Slab Deformation for Jointed Plain Concrete Pavements

Slab curvature, which represents the response of concrete pavement slabs to environmental loads, influences the location and magnitude of critical slab stresses and affects long-term pavement performance. The purpose of this study was to measure the changes in temperature and moisture profiles in a newly constructed concrete pavement and to determine both the overall deformed shapes of the slabs as well as the relative contributions of built-in and transient environmental effects over time. Data were collected from an instrumented jointed plain concrete pavement (JPCP) over a 2-year period. Slab curvatures were computed or predicted using measurements of temperature and moisture conditions in the slab, static strain measurements, and pavement surface profile measurements. It was found that the additional restraint provided by the dowel and tie bars does not appear to significantly reduce slab curvature resulting from daily temperature fluctuations or from reversible drying shrinkage. It does have a substantial effect on reducing slab curvature attributable to long-term drying shrinkage. It was also found that the Mechanistic-Empirical Pavement Design Guide default value is close to that measured in this study for the restrained slab but does not appear to be appropriate for unrestrained (i.e., undoweled) slabs.

Analysis on the Influence of Dowel Bar at Joints on Load Stress of Pavement Slab in the Pumping Area

A 3D finite element model is used to investigate the state of load stress developed in concrete pavement with dowel bar under the effect of typical pavement damages of pumping area of slab corner and pumping area of transverse joints edge. The results indicate that slab corner stress tends to decrease with the increase of slab thickness and possesses a nonlinear growth as pumping area increases; when the pumping area of slab corner is less than 1.5m×1.5m, the maximum pavement slab tensile stress is less than or close to the load stress in critical loading position. Stress in transverse joints edge also grows in a nonlinear tendency and axle load also grows gradually with the expansion of pumping area, of which the slope of the curve in the relationship between stress and void size is much greater. Whether it is a pumping area of slab corner or pumping area of transverse joints edge, pavement slab deformation and stress are significantly reduced after setting the dowel bar. Therefore, dowel bar can improve the stress state of concrete pavement obviously.

Strengthening of flat slabs with post-tensioning using anchorages by bonding

This work aims to study a new flat slab strengthening technique based on post-tensioning with anchorages by bonding using an epoxy adhesive. The main advantages of this technique over the traditional prestress strengthening systems that use mechanical anchorages are that it does not need external permanent anchorages, meaning that the forces are introduced into the concrete gradually instead of being localized, thereby preserving aesthetics and useable space. The seven tested slab models show that this technique meets its objective as it is able to reduce reinforcement strains at service loads by up to 80% if the strengthening technique is applied in two directions and slab deformations by up to 70%, consequently making crack widths smaller. It can also increase punching load capacity by as much as 51% when compared to non-strengthened slabs. The results are compared with the EC2 (2004) [20], ACI 318-08 (2008) [23] and MC2010 (2010) [21] provisions. The main conclusions are that this strengthening technique is effective regarding ultimate and serviceability states and that it represents an advance in RC slab strengthening techniques.